The present invention relates to a multilayer, preferably sealable laminated film having a barrier layer therein, as well as to a process for its manufacture and use.
A multilayer film having a barrier layer made of a material such as that used in the present invention is described in German Offenlegungsschrift No. 26 44 209 (equivalent to British Patent Specification No. 1,567,189). The disclosed film has a multilayer structure including a base comprised of polypropylene, an intermediate layer comprising a modified polyolefin provided on the base film, and a barrier layer to reduce oxygen permeability, with a heat seal layer optionally applied to the barrier layer. The film is prepared, according to the aforementioned German Offenlegungsschrift, by applying to the transversely or longitudinally axially oriented polypropylene base film a two-layer melt comprising the polymers of the intermediate layer and the barrier layer. The composite film thus obtained is then oriented by stretching it in the transverse direction. The heat sealable layer is applied subsequently, i.e., after the preparation of the three-layer composite film, in a further step and is therefore essentially unoriented. As a result, different orientation values are obtained for the layers of the base film, the intermediate/barrier layer, and the heat seal layer, respectively.
It has now been found that the above-discussed film is frequently incapable of satisfying requirements concerning gas barrier properties, water resistance, and other physical properties, which requirements have become increasingly stringent.
To improve the sliding properties of the film disclosed by German Offenlegungsschrift No. 26 44 209, European Patent Application No. 0 062 815 describes a process to modify the outer sealing layer by means of special additives. The disclosed modification of the outer sealing layer does not improve the gas barrier properties and water resistance of the film. Furthermore, the individual layers are not oriented under the same conditions.
On the other hand, the existing sealable, multilayer films having a barrier layer comprised of ethylene-vinyl alcohol copolymers cannot be produced by extruding all of the layers simultaneously to obtain an orientation of all layers by stretching under identical conditions.